This application is directed to the art of pipe joints and couplings and more particularly to joint or coupling structures for plastic pipe or tubing. The invention is particularly applicable to internal couplers for connecting adjacent ends of corrugated plastic pipe or tubing and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications and may be incorporated as an integral part of the tubing, may be sized and configured to accommodate connecting tubing of different sizes and shapes with associated structures, may be used with other fittings, and the like.
Corrugated plastic pipe or tubing is widely used for many types of domestic, agricultural, and industrial drainage and waste disposal systems. This pipe or tubing is typically molded of high density polyethylene, polyvinyl chloride, or the like. The pipe itself is commonly cylindrical, although other shapes are also used, and has corrugated internal and external wall surfaces defined by adjacent circumferentially extending, longitudinally spaced peaks and valleys. When installing corrugated pipe or tubing in the ground, it is often necessary to connect the ends of two tubing lengths or to connect the end of one tubing length with an associated structure.
Heretofore, various types of joints or couplers have been developed for connecting the ends of the tubing. One particularly successful coupler is described in U.S. Pat. No. 4,247,136, issued Jan. 27, 1981 to James L. Fouss, Donald W. Sting, John J. Parker, and Robert Biango, and assigned to the assignee herein. This prior art coupler is particularly advantageous for use in conjunction with automated conduit laying machinary. The coupler provides a secure connection which is not readily separated by automated, machine handling. Further, the coupling creates an internal connection without external features which may interact adversely with the automated handling machinary.
Although this prior art internal coupler has been relatively successful, it is relatively time consuming and labor intensive to manufacture. Commonly, the couplers are individually molded. After the molding operation, end walls which are formed by the mold ends are sawn off and slots around the outward projecting cleats are individually cut or punched.
The present invention contemplates a new and improved coupler which is adapted to be manufactured by continuous blow molding techniques. The invention further contemplates a continuous blow molding apparatus and method for manufacturing couplers.